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Abstract

Metal masks are lifted off Si wafers by means of a ram. The ram, which is hydraulically guided, is provided with suction ports connected to a vacuum source.

Country

United States

Language

English (United States)

This text was extracted from an ASCII text file.

This is the abbreviated version, containing approximately
65% of the total text.

Lift-Off Device for Metal Masks

Metal masks
are lifted off Si wafers by means of a ram.
The ram, which is hydraulically guided, is provided with suction
ports connected to a vacuum source.

The PbSn end
metallization of wafers with C4 contacts is
evaporated through a metal mask. The
metal mask is initially
adjusted on the wafer surface. The
openings in the mask coincide
with the electrical vias on the wafer.
In the subsequent evaporation
step, the PbSn is deposited on the wafer only in the region of the
mask openings. After completion of
evaporation, the mask is lifted
off the wafer, with the PbSn pads (C4 contacts) remaining on the
wafer.

The oblique
angle of incidence of the PbSn vapor along the
wafer periphery leads to deposition at the edges of the openings
particularly on large-diameter wafers.
The PbSn deposited in the
mask openings on the wafer and on the mask surface forms a continuous
layer along the edges of the openings.
As a result of this and
differential expansion of wafer and mask caused by heating during
deposition, the mask is difficult to lift off.
The adhesion of the
mask along the edge and in the center of the wafer differs; it
frequently happens during lift-off that the mask is bent or that
twisting occurs between the mask and wafer, with the inherent risk of
PbSn pads being torn from the vias. Even
pads that become only
partly detached may lead to premature chip and functional failure.